April 28, 2017

Ticks

Ticks (Tick Bites)

What diseases do ticks transmit (act as vectors) to humans?

Although most tick bites do not transmit pathogens, some bites do. It is not possible to determine if a tick is carrying pathogens visually. The following is a list of all of the major tick-borne diseases, the usual tick vector(s), and the pathogen(s) the tick transmits that may occur in the United States.
  • Tularemia -- Dermacentor variabilis (American dog tick; several species are also known as a wood tick) (hard tick) and Amblyomma americanum or lone star tick (hard tick) -- vectors for Francisella tularensis bacteria
  • Anaplasmosis (human granulocytic anaplasmosis or HGA) -- Ixodes species (hard tick) -- vectors for Anaplasma phagocytophilum bacteria
  • Colorado tick fever -- Dermacentor andersoni (hard tick) -- vectors for Coltivirus, a RNA virus
    Powassa encephalitis -- Ixodes species and Dermacentor andersoni (both hard ticks) -- vectors for Powassan encephalitis virus, an RNA arbovirus
  • Babesiosis -- Ixodes species (hard ticks) -- vectors for Babesia, a protozoan
  • Ehrlichiosis -- Amblyomma americanum or lone star ticks; see photo below with "lone star" mark on the dorsal surface (hard ticks) -- vectors for Ehrlichia chaffeensis and Ehrlichia ewingii bacterial species
  • Rocky Mountain spotted fever -- Dermacentor variabilis (American dog tick, see picture below) and Rocky Mountain wood tick (Dermacentor andersoni) (hard tick) are the primary vectors and occasionally the brown dog tick (Rhipicephalus sanguineus); Amblyomma cajennense (hard tick) is the vector in countries south of the U.S. -- vectors for Rickettsia bacteria
  • Lyme disease -- Ixodes species including deer ticks or also known as black-legged ticks (hard ticks, see photo below) -- vectors for Borrelia species of bacteria
  • Heartland virus -- a viral disease discovered in 2012 transmitted by Amblyomma americanum or lone star tick
  • Tick-borne relapsing fever -- Ornithodoros moubata or African tick; see illustration below (soft tick) -- vectors for Borrelia species of bacteria
  • Q fever -- Rhipicephalus sanguineus, Dermacentor andersoni (see photo below), and Amblyomma americanum (all three are hard ticks) -- vectors for Coxiella burnetii, a bacterium
  • Southern tick-associated rash illness (STARI) -- Amblyomma americanum or lone star tick (hard tick) -- infectious agent not yet identified according to U.S. Centers for Disease Control and Prevention (CDC)

Tick species and the diseases that they carry.

This list shows that some ticks (for example, Ixodes) can transmit more than one type of pathogenic microbe (virus, bacteria, and protozoa). It is possible to transmit more than one pathogen in a single tick bite, although this rarely occurs. Outbreaks of tick-related illnesses follow seasonal patterns (about April to September in the U.S.) as ticks evolve from larvae to adults.

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Reviewed on 8/19/2016